Can We add Two diff. zones with diff SHR 2

[offshorehvac]

Hi Friends

I am reviewing load calcutions submitted by a vendor

Application is comfort HVAC for Living Quarter on an offshore Rig.
There are about 90 small rooms being served by a large common AHU

Vendor has divided the load for rooms into two groups

In group 1, about 40 rooms and in group 2 about 50 rooms are considered. Then psychrometric analysis is performed for each group using air flows and average SHR for each group. Once the psychrometric is done, vendor has added the flow and capacity to arrive at the total capacity of one AHU serving all the 90 rooms

My question is that
-Is the right way to do?
-Can we add the capacities or psychromteric analysis should be done for the one single AHU which will serve all the rooms
-I know SHR plays an important roll in equipment selection. When calculations are done for two groups, the RSHR for group -1 is 0.85 and for group-2 is 0.9. But when we consider all the 90 rooms as one system then the RSHR is about 0.879

If this is acceptable then it is OK, If not then What should be my comment on the vendor calculations?

Can we add SHR

 

[imok2]

Here's what I think about Air Conditioning load calculations. It's not an exact science so if you calculate a load for a 0.9 SHR that, must be based on the assumption that the peramaters are gonna stay fairly constant. But we know that conditions are not always constant and the SHR could be different and other times so how much difference if you split the difference to 87.5%? on the other hand you can always put in two units and go for the vendors numbers

 

[ChrisConley]

Multi-zone reheat would be the easiest way to achieve the two calculated conditions. Set the AHU for the worst case scenario, and provide two zones of reheat.

 

[quark]

imok and Chris, stars to both of you.

Offshorehvac,

imok2 hit the nail on the head regarding redundancy in the design. Somewhere or the other, we have to take chances. For example, you are adding the loads of first forty rooms and calculating the SHR.When you check individual room sensible and latent loads, you may get as many as 40 ratios. Likewise, it is same for the second group of 50 rooms.

There is always a question about what can be the correct SHR and accordingly what is the correct ADP. You can answer this question, indirectly, by specifying a range for DBT and RH for individual rooms. The somewhat incorrect ADP specification will be offset by the range.

If you want to play a safe hand, go with Chris's suggestion. Chose coil ADP corresponding to the lower SHR vaule and go for zone reheating.

 

[AbbyNormal]

size it based on the lower SHR, maybe you have a little more capacity needed to get all the sensible cooling

it probably peaks in the late afternoon, so even the guys on the midnight shift are up and about and most likely not in their rooms

sounds like not much of a challenge with humidity, what is the load like when it's cloudy out and the surrounding air has the same dewpoint as the surface of the sea

Take the "V" out of HVAC and you are left with a HAC(k) job.

 

[AbbyNormal]

why reheat?



Take the "V" out of HVAC and you are left with a HAC(k) job.

 

[AbbyNormal]

I would be more worried if the two SHRs were 0.75 and 0.65

Take the "V" out of HVAC and you are left with a HAC(k) job.